1972).) It is also possible that differences in 

 habitus account for this enigma. Loeblich et al. 

 (1968) report that solitary cells present in cultures 

 were unable to form colonies, and under certain 

 conditions colonies reproduced themselves as 

 "clusters of cells" or "a solitary pattern of growth" 

 occurred. If the occurrence of variations in habitus 

 correctly explains these biogeographical issues, 

 then the factors triggering colony formation be- 

 come of interest. Upwelling does not appear to be 

 detrimental in this regard, at least during its 

 initial stages in the survey area. 



From its size, thickness, and concave-convex 

 shape, it might a priori be presumed that 

 Planktoniella muriformis is particularly well 

 adapted for flotation and has a near-surface niche. 

 However, the equal distribution in colony abun- 

 dance in the upper 40 m is noteworthy, and con- 

 trasts to Planktoniella sol's concentration in the 

 upper 20 m (Figure 2; Table 4). 



Coscinodiscus (Brenneckella) 

 eccentricus 



In the Gulf of Panama a unique centric diatom 

 was found identified as Brenneckella sp. (Smayda 

 1966). It was characterized by an "outer, gelatin- 

 ous" ring surrounding the girdle region in or on 

 which coccolithophorids and other particulate 

 matter were embedded. This organism was also 

 commonplace in the present material (Tables 1,4), 

 and grew actively in one experiment when 2.9 

 divisions/day were measured (Smayda in press b). 

 Gaarder and Hasle (1961) have reviewed its tax- 

 onomic history, the limited information on its dis- 

 tribution, and the potential relationships between 

 the attached organisms and the host diatom. 

 Based on electron microscopy, they concluded that 

 the two species of Brenneckella described earlier 

 are conspecific with Coscinodiscus eccentricus , a 

 synonomy which is followed here. Nonetheless, it 

 is listed separately as Coscinodiscus (Bren- 

 neckella) eccentricus in Tables 2 and 4 where 

 mean values for the Coscinodiscus spp. are given. 



Gaarder and Hasle suggest that the attachment 

 of cocolithophorid cells to this diatom is a mere 

 agglutination without any symbiotic significance. 

 While this may be so, the relationship still re- 

 mains intriguing. One may ask why other 

 Coscinodiscus species, or centric diatoms, includ- 

 ing Planktoniella sol characterized by an outer 

 membrane, seemingly are invariably devoid of 

 such epibionts. 



FISHERY BULLETIN: VOL. 73, NO. 1 



DISCUSSION 



Allen (1924, 1934, 1938) and Cupp (1930, 1934; 

 Cupp and Allen 1938) carried out a long-term sur- 

 vey (approximately 1921 to 1937) of the net phyto- 

 plankton in the coastal, surface waters of southern 

 and Baja California. These data are valuable prin- 

 cipally in their suggestion that the net diatom 

 community in these waters from San Diego to the 

 Gulf of Panama is similar, inclusive of the Gulf of 

 California (Cupp and Allen 1938; Gilbert and 

 Allen 1943). Subsequent quantitative observa- 

 tions in the Gulf of Panama (Smayda 1963, 1966), 

 net collections in the Gulf of California (Round 

 1967), and the present survey generally support 

 this. 



Diatoms dominated the net community (Table 

 4) in response to upwelling, then in its early 

 stages. A red-tide outbreak occurred during mid- 

 April in the survey area following a temporary 

 subsidence of upwelling (Walsh pers. commun.). 

 During the MESCAL I survey of 1972 in this same 

 region the dinoflagellate Gonyaulax polyedra 

 was dominant in March (Walsh et al. 1974). Its 

 abundance then also probably reflects the occur- 

 rence of limited, if any, upwelling. Thus, annual 

 variations in time of inception of upwelling in 

 these waters, as well as variations within a given 

 upwelling cycle, are reflected in the relative im- 

 portance of dinoflagellates vis-a-vis that of dia- 

 toms. An abundance of diatoms will be an indi- 

 cation of nutrient enrichment, as is generally 

 observed in upwelled waters. j 



The species composition of the diatom commu- " 

 nity is of considerable interest, given the observa- 

 tions of Longhurst et al. (1967). They reported that 

 Coscinodiscus species, especially C. eccentricus, 

 were important dominants of the upwelling com- J 

 munities in June and August 1964 near Mag- " 

 dalena Bay, lying south of the present survey 

 area. Blooms of this genus are of exceptional in- 

 terest. Coscinodiscus, a priori, is not generally 

 expected to occur in great abundance pelagically 

 in unmodified coastal and oceanic water masses.  

 This is generally confirmed by worldwide observa- 1 

 tions, as reported in the extensive literature on 

 phytoplankton surveys. The periodic, enormous 

 spring blooms of Coscinodiscus concinnus in the 

 North Sea are noteworthy and puzzling (Gr0ntved 

 1952). 



This interest in local species composition is sus- 

 tained, given the remarkable occurrence and 

 abundance of the red crab, Pleuroncodes planipes. 



46 



